Tagger hodoscope and photon beam monitoring D Sober

Tagger hodoscope and photon beam monitoring D. Sober, F. Klein (CUA) Tagger Review, Jan. 23 -24, 2006

Hall-D tagger • two-magnet design • horizontal deflection • photon spectrum: coherent and incoherent bremsstrahlung primary e-beam deflected e-beam

data taking at E 0=4 -6 Ge. V coh. peak at 1. 3 -2. 2 Ge. V 50μm (20μm) diamonds (mosaic spread<10μrad) Enhancement (after collimation) Coherent Bremsstrahlung in Hall B Coh. peak at 2. 1 Ge. V Coh. peak at 1. 3 Ge. V Coh. peak at 1. 5 Ge. V

Crystal alignment Hall-B alignment via “Stonehenge” method: Hall-B goniometer (6 d. o. f. ) for crystal positioning

Hall-D tagging system • • Beam energy E 0=12 Ge. V coherent peak at 7 -10 Ge. V microscope tags ~600 Me. V near coh. peak fixed hodoscope (tags 3. 0 -11. 4 Ge. V) – located 20 cm from true focal plane (to allow for microscope motion) Requirements for fixed hodoscope: • crystal alignment → special runs at reduced rate • photon beam monitoring → at full production rate

Rate estimates (1) assuming: • Jlab beam conditions • 20μm crystal • coh. peak at 9. 6 Ge. V • collimation to 0. 56 θchar • microscope tags 9. 0 -9. 6 Ge. V – 25 MHz tagged photons in microscope – 10 MHz tagged photons on target (40% collimation)

Rate estimates (2) Rate per cm counter width full energy range Note: Structures above 10. 5 Ge. V washed out due to dispersion high energy range

Proposal for fixed array: • • • 140 counters at 60 Me. V (0. 005 E 0) steps full coverage: 9. 0 – 11. 4 Ge. V (40 counters at 60 Me. V spacing) sampling: 3. 0 – 9. 0 Ge. V (100 counters at 60 Me. V spacing) tag rate sample fraction counting rate (at 60 Me. V spacing) (at 10 MHz on target) 0. 28 cm 0. 42 ~2 MHz 60 0. 39 cm 0. 55 ~2 MHz 5. 0 50 0. 50 cm 0. 67 ~2 MHz 6. 0 45 0. 58 cm 0. 73 ~2 MHz 7. 0 40 0. 73 cm 0. 83 ~2 MHz 8. 0 40 0. 81 cm 0. 83 ~2 MHz 9. 0 – 11. 4 22 – 26 1. 1 – 3. 7 cm 1. 0 ~1. 4 MHz Eγ (Ge. V) (k. Hz/Me. V) 3. 0 80 4. 0 (above coh. peak) counter width

Fixed array: Sampling at lower energies purpose: alignment (not used during production runs) option to insert additional counters later crystal alignment with 60 Me. V sampling full coverage Relative intensity photon energy (Me. V))

Fixed array: Sampling at lower energies (2) problem to analyze spectra when sampling? • • structures less pronounced esp. difficult when crystal far off-axis – but feasible with ~50 -60 Me. V sampling crystal alignment with 60 Me. V sampling full coverage (raw) full coverage (analyzed)

Fixed array: full coverage in endpoint region Purpose: alignment of diamond crystal monitoring of structures during production runs options for high rates: number of counters energy bite per counter width rate at 10 MHz tags on target rate at 100 MHz tags on target 40 60 Me. V 1. 1 – 3. 7 cm 1. 4 MHz 14 MHz 80 30 Me. V 0. 6 – 1. 8 cm 0. 7 MHz 120 20 Me. V 0. 4 – 1. 2 cm 0. 5 MHz

Summary Fixed tagging hodoscope for Hall D: purpose: • monitoring of photon beam • crystal alignment proposal: • full coverage at 9. 0 – 11. 4 Ge. V • sampling at 3. 0 – 9. 0 Ge. V (60 Me. V momentum bites) • option to add counters for full coverage (at lower production rates) • scintillation counters (0. 5 cm thick, 4 cm high) • width: 0. 28 – 3. 7 cm (adjusted to rates of ~2 MHz/counter for 10 MHz on target) Option: Monitoring of collimated photon beam via pair spectrometer